1. Field of the Invention
The present invention relates to glass reinforced molding compositions based on oxymethylene polymers, and particularly compositions comprising a copolymer of trioxane and a cyclic ether and/or cyclic acetal. The present invention relates in particular to such glass reinforced compositions exhibiting an increased retention in properties such as tensile strength.
2. Description of the Prior Art
Oxymethylene polymers, having recurring --CH.sub.2 O-- units, have been known for many years. They may be prepared by polymerizing a source of oxymethylene units such as anhydrous formaldehyde or trioxane, i.e., a cyclic trimer of formaldehyde.
High molecular weight solid polyoxymethylenes have been prepared by polymerizing trioxane in the presence of certain cationic catalysts, and may also be prepared in high yields and with rapid reaction rates by the use of catalysts comprising boron fluoride coordination complexes with organic compounds, as described, e.g., in U.S. Pat. No. 2,989,506 of Donald E. Hudgin and Frank M. Berardinelli. Boron fluoride gas is also a rapid and effective catalyst, as disclosed in U.S. Pat. No. 2,989,507 of Hudgin and Berardinelli. Other suitable catalysts are disclosed in the article by Kern et al in Angewandte Chemie, 73, (6), pages 176-186 (March 21, 1961).
The usefulness of oxymethylene copolymers in molding compositions and methods of preparing oxymethylene copolymers have also been known for years. For example, U.S. Pat. No. 3,275,604 discloses a moldable polymer comprising oxymethylene groups and oxyethylene groups, with said oxyethylene groups having a --CH.sub.2 OR group pendant therefrom, which may be prepared by polymerizing a source of oxymethylene units such as trioxane with a glycidyl ether.
U.S. Pat. No. 3,519,696 discloses copolymers of trioxane with cyclic ethers or cyclic acetals. The copolymers can be advantgeously prepared from mixtures of from 50 to 99.9% by weight of trioxane and from 0.1 to 50% by weight of cyclic ethers or cyclic acetals in the presence of from 0.0001 to 1.0% by weight of cation-active catalysts. The polymerization is conducted at temperatures in the range of from 62.degree. to 115.degree. C. in containers made from thermoplastic materials, which are crushed subsequent to the polymerization and then worked up to recover the copolymer.
U.S. Pat. No. 3,631,124 discloses a thermoplastic molding composition having improved impact strength, which compositions are obtained by mixing a polyoxymethylene such as a copolymer of formaldehyde or trioxane, with a polyether, for example, polyethylene oxide. Suitable copolymers include copolymers of trioxane with cyclic ethers, for example, ethylene oxide, or cyclic acetals, e.g., 1,3-dioxolane.
Oxymethylene terpolymers and the preparation thereof are also known to the art. For example, U.S. Pat. No. 3,385,827 discloses trioxane terpolymers obtained by copolymerizing under conditions commonly used for the production of trioxane copolymers (i) trioxane, (ii) a cyclic ether and/or cyclic formal, e.g., such as ethylene oxide, dioxalane and diethylene glycol formal, and (iii) a bifunctional diglycide such as a diglycidyl ether of ethylene glycol. In U.S. Pat. No. 3,627,850, there is also disclosed a terpolymer of 100 parts by weight of trioxane, two parts by weight of ethylene oxide and 0.1 part by weight of butanediol diglycidyl ether, the terpolymer being in mixture with a trioxane copolymer.
U.S. Pat. No. 3,848,021 discloses an oxymethylene terpolymer of trioxane, a cyclic ether or cyclic acetal and a polyether. The terpolymer is employed as a nucleating agent in a poly(oxymethylene) in order to increase the crystallization speed thereof and hence render the crystal structure of injection molded articles made therefrom more uniform. The presence of the nucleating agent further results in a decrease of the size of spherulites and thus in an improvement of the mechanical properties of shaped articles manufactured from the disclosed molding composition, which is composed of (a) from 99.9 to 80 weight percent (1) of a homopolymer of formaldehyde or trioxane, or (2) of a copolymer obtained by polymerizing a mixture of from 99.9 to 80 weight percent of trioxane and from 0.1 to 20 weight percent of a cyclic ether having from 3 to 5 ring members, or a cyclic acetal differing from trioxane having from 5 to 11 ring members, or a linear polyacetal, and (b) from 0.1 to 20 weight percent of a copolymer obtained by polymerizing a mixture of from 99.9 to 50 weight percent of trioxane and from 0 to 20 weight percent of a cyclic ether having from 3 to 5 ring members, or a cyclic acetal having from 5 to 11 ring members, or a linear polyacetal, and from 0.1 to 30 weight percent of a polyether.
Molding compositions exhibiting an increased retention of properties, such as tensile strength, and particularly molding compositions containing glass fiber reinforcement that exhibit this characteristic, are highly desirable. This is also true for molding compositions based on polyoxymethylene copolymers, wherein increased property retention can result in longer and improved performance of shaped articles made therefrom. The search for such molding compositions has been continuous, and hence, the attainment of a molding composition based on oxymethylene polymers having improved property retention could be of great benefit to the art.
Accordingly, it is an object of the present invention to provide a polyoxymethylene copolymer comprising composition which exhibits improved property retention, and in particular, improved tensile retention.
It is another object of the present invention to provide a polyoxymethylene copolymer composition having glass reinforcement which exhibits improved property retention.
It is still another object of the present invention to provide a glass reinforced molding composition based upon oxymethylene polymers which can produce shaped articles capable of improved performance, e.g., a longer useful life.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.